1. Field of the Invention
The present invention relates to a method of and an apparatus for measuring film thickness. In particular, the present invention relates to a method of and an apparatus for measuring the thickness of a thin film which is an uppermost layer of a sample having two or more stacked thin films.
2. Description of the Prior Art
In general, interferometry is widely used to measure the thickness of a transparent thin film such as a silicon oxide film formed on a silicon substrate. The technique is used in a non-contact manner in an inspection step of a semiconductor fabricating process or the like.
To measure the thickness of the transparent thin film, visible light is applied to the sample and the spectrum of light reflected by the sample is detected.
FIGS. 1A to 1C illustrate three general types of waveforms representing spectra of light reflected by samples having a transparent thin film to be measured when the samples are irradiated with visible light. The thickness of the transparent thin film is determined according to the type of spectral data actually detected, as follows: